$ { {-4} \times \left[\begin{array}{rrr}{3} & {1} & {2} \\ {0} & {1} & {4}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-4}\times{3} & {-4}\times{1} & {-4}\times{2} \\ {-4}\times{0} & {-4}\times{1} & {-4}\times{4}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-12} & {-4} & {-8} \\ {0} & {-4} & {-16}\end{array}\right]}$